Current limiter system



Aug. 28, 1951 v. A. SANDER CURRENT LIMITER SYSTEM Filed NOV. 28, 1949 FIGI.

a! 271 FIG Z, 6

Patented Aug. 28, 1951 UNITED STATES PATENT OFFICE CURRENT LIMITER SYSTEM Vernon A. Sander, St. Louis, Mo., assignor to W. N. Matthews Corp corporation of Missouri Application November 28, 1949, Serial No. 129,810

4 Claims. 1

This invention relates to current limiter systems, and more particularly to circuits including thermostatic current limiters for use in a power distribution system to limit the amount of current drawn by an individual consumer.

This invention is an improvement upon the current limiter circuit disclosed in the application of Carl E. Mosley for Current Limiter, Serial No. 43,890, filed August 12, 1948, now Patent No. 2,518,361, dated August 8, 1950, and in a division of the said Mosley application, Serial No. 129,775, filed November 28, 1949.

The principal object of the invention is the provision of a circuit arrangement utilizing a thermostatic current limiter for use in a three-wire distribution system for automatically disconnecting a secondary or dispensable load element, such as an electric water heater, if the total load drawn by a consumer should exceed the peak limit. A consumer may have, for example, primary load elements such as lights, an electric range, and other electric appliances, and a dispensable or secondary load element, such as an electric water heater, all drawing current from a three-wire supply system. With the present invention, the heater, operation of which may be most conveniently discontinued as regards the other load elements, may be connected to draw current at the full voltage across the outer conductors of the system as long as the total load on one leg of the system does not exceed the peak limit, automatically disconnected whenever the total load exceeds the peak limit, and automatically restored to service when the load drops below the peak limit.

In general, a wiring system of this invention comprises a three-wire single-phase circuit, supplied by a three-wire single-phase service, and including the consumers primary load elements. The thermostatic part of the current limiter is connected in one leg of the circuit to act in response to current drawn in that leg. A secondary load element, such as a water heater, is connected across the outer legs of the circuit in a line including the switch of the current limiter, the arrangement being such that the switch opens and disconnects the secondary load element if the current drawn in the leg in which the thermostatic device is connected exceeds the peak limit. Other features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter oration, St. Louis, Mo., a

2 described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing, in which one of various possible embodiments of the invention is illustrated,

Fig. 1 is a view in side elevation of a current limiter used in a system of this invention;

Fig. 2 is an end elevation of Fig. 1 as viewed from the right;

Fig. 3 is a plan view of Fig. 1;

Fig. 4 is an enlarged fragmentary section taken on line 4--4 of Fig. 3; and,

Fig. 5 is a wiring diagram illustrating a mode of connecting the current limiter shown in Figs. 1 to 4 in a consumers circuit.

Similar reference characters indicate corresponding parts throughout the several views of the drawing.

Referring to the drawing, a current limiter used in this invention is shown to comprise a base 1 consisting of a circular metal plate. This carries three main terminals 3, 5 and 1. Each of these main terminals is fixed in an insulation bushing 9 secured in an aperture in the plate to insulate the terminals from the plate. Each main terminal, as illustrated, consists of a flat metal strip, and each bushing has a narrow rectangular opening ll receiving its respective strip, with the strips extending above and below the plate. At 13 is shown an insulation panel mounted on and above the base I by means of posts l5 and 11. The post 15 is a conductor to serve as a terminal and is bolted to the upper end of the terminal 3 as indicated at 19-. The post [5 is formed with a step 2| on which the panel l3 bears, the panel being bolted on the step as indicated at 23. The post I5 extends upward from the step above the panel through a slot 25 in the panel, and is formed with an outwardly projecting car 21 at its upper end. The post 11 does not carry current.

At 29 is shown a conductive terminal post which extends upward from the panel l3 parallel to the post I 5. The post 29 is secured at its lower end to the panel as indicated at 3| and has an outwardly projecting ear 33 at its upper end at the level of the ear 21 on the upper end of the post I5. Current-heated thermostatic blades 35 and 31 are secured at one end upon the ears 21 and 33, respectively, as by welding, and are cantilevered outward in the same direction from the ears in coplanar, laterally spaced, parallel relation. The two blades are of substantially the same length and have substantially the same temperature-displacement characteristics. Each blade is arranged to bend up upon heating, down upon cooling. For example, the blades may be bimetallic with their low coefficient of thermal expansion sides on top.

The free ends of the blades are connected by a conductive connecting member 393. This comprises a bar bent to have a U-shaped central portion M with flanges Q3 extending outward from the ends of the arms of the U. The flanges G3 are secured to the upper sides of the free ends of the blades as by welding with the U-shaped central portion opening downward. A block of thermal (and electrical) insulation 05 is secured within the U by means of bolts WI. Member 39 is free to move up upon heating of blades 35 and 3?, down upon cooling. I

A snap-acting switch 49 is mounted on the panel I3 between the posts I5 and 29. This switch is of a type which is conventional in the art, having an insulation case 5| housing the switch contacts and the snap-acting switch-actuating a mechanism and vhaving an operating button 53 Fig. 4) projecting upward through an opening in the top of the switch case. It also has a resilient lever 55 fixed at one end to, the top of the case as indicated at El and extending over the button. The lever 55 is. normally raised and may be pushed downward,,against its inherent bias to push in thebuttonandopen the switch, the switch being normally closed. When the lever is raised, the button moves upward and the switch re-closes.

The switch is held;upon the panel i3 between conductive switch-holding members 5% and GI secured. to the paneltoiextend along the sides of the switch case. 63. which reaches through the slot 25. in the panel and which is held in place by the bolt 23 holding the panel on the step 2i. This also .servesv electrically toconnect'the. post Iii andthemember 5:5. The member 59 also hasa portion be reaching under the switch case which is connected to one terminal 66 .of the. switch....The..member BI is fastenedto the, panel at El and has a portion be reaching under the switch case whichis connected to the. otherterminal E of theswitch. The switch. case is held in place between the members 59 and GI by meansof pins lI extending from the case throu h holes in the members.

A thermostatic. blade, element I3.is pivoted at I tothe insulation block 35.carried by the member .39 andv extendsirom thepivot under the block and centrally between theblades 35 and El. The blade l3 carriesaflnger ll at. its free end which bears on theswitch-actuating lever The blade 73 is pivoted. at if; to a hinge leaf l9 fixed to the bottomof the block .45 by a bolt 88, the pivotal axis being transverse to the center line between the blades 35 and 31. The blade '53 is arranged so that its free end carrying finger ll moves upward Onheating, downward on cooling. For example, the blade 63 may bea bimetallic blade with its low coefficient of thermal expansion side on top. As. illustrated, the blade 73 is shorter than theb1ade's135 and 3t and. it is made thicker thanbladesgss and 3'5.

The finger I? on the free end of the bladelli is adapted to be maintained in pressure engagement with the operating lever 55 of switch as by means of a screw 8| threaded in an ear 83 formed on the member .30, the screw being located between the pivot 151and the free end of the blade I3 near the pivot... The screw has atip 85 of thermal insulation bearing against the upper side of the blade .13.. Adjacent its upper end, the screw has a flange 81 (Fig. l). Bearing Themember 53. has a portion grounded by the neutral "wire I07.

against the top of this flange is a head 89 and bearing against the bottom of the flange is a stop disc 9I larger than the head having a notch 93 in its periphery (Fig. 3). The head and disc are tied together by screws 95, which releasably clamp them against the flange so that, by loosening the screws 95, the angular position of the head and disc on the screw 9I may be varied. A stop pin 91 extends upward from the member 39 through the notch 93 to limit the rotation of the screw to the arcuate extent of the notch. It will be seen that the pressure of the finger TI on the "lever 55 may be varied by turning the screw 8L to move it up or down.

The main terminal 5 is electrically connected to the terminal post 29 by means of a conductive rod.99.. The main terminal I is electrically connected to the member 6| by means of conductive rodIOI. The main terminal 3, as previously described, is directly connected to the terminal post I5.

The blades 35 and 31:, "the connecting member 39 and the blade I3 formagenerally Eeshape'd thermostatic. device having its outer currentcarrying legs 35 and 37 joinedatfone of their ends by the electrically conductive. connecting member 39'and its central .thermostaticleg I3 extending from the-connecting member 39 between the outer legs, and thermallyin'sul'a'ted from the member 39 by the. block 45.. .The outer'legs are fixed at their outer ends tothe posts I5 and'29, which form terminal elements, and 'a're'cantilevered outward from the terminal'posts I.5and 29 so that the connectingmember is. freely mov able in response to temperaturechangeas the outer legs 35 and3'I flex. As herein illustrated, the connecting member 39 moves. up when legs 35 and 31 are heated, down when theycool.

Fig. 5 illustrates a circuit. arrangement of this invention wherein the above-described current limiter is connected, in a three-wire single-phase system supplying a consumers load requirements shown as including an electric range R, an elec tric water heater H, lights and other loadelements L. The supply circuit or service is shown at S, with the neutral wire of the circuit shown as adotted line. At Mis shown the usual main electric meter, .from which lead outer conductors Hi3 and. I05 and a neutral wire I07, the latter being shown as a dotted line. The conductor I03 is connected .to the terminal 3 of the current limiter. A conductor I'09is connected to the terminal 5 of the current limiter. The range R is connected across conductors IDS-and I09 and It will be understood that some types of ranges have switches permitting connection of the heaterelement to either the outer legs or to an' outer leg and the neutral so as to provide difierentamounts of heat. The heater'H is connected ac'ross'con ductors I03 and I05 in a circuit including the switch 49 by means of a wire I-II connected to one terminal of the heater and to the terminal l of the current limiter'and a wire H3 connected to the other terminal of the heater a'nd'to the wire I05 at H5. The heater is' grounde'd by a neutral wire Ill connected to the neutral wire H0? at H9. The load'elementstL are connected in two separate circuits I2I and. I23, which are generally of approximately" equal load, one being connected across conductor I09 and neutral wire I01 and the other across conductor I05 and neutral wire I01.

'In operation, current flows in seriesthro'ugh thermostatic element 35, member stand thermo static element 31 01' the E-shaped thermostatic device. The thermostatic elements 35 and 31 are thereby heated to a degree dependent upon the current value. The value of the current flowing through the thermostatic device is dependent upon the load imposed by the range R and the load elements L in circuit 12!. Whenever the current drawn by the range and load elements L in circuit l2! exceeds a predetermined peak value, as determinedby the setting of the screw 8| the thermostatic elements 35 and 31 are heated to such an extent that the member 39 moves upward and acts through the blade '13 to open the switch 49, thereby disconnecting the water heater H. When the current drops below the peak value, the elements 35 and 31 cool, member 39 moves downward, and the switch 49 closes to re-connect the heater H. The arrangement is such that the customer may, if desired, voluntarily reduce the load imposed by the range R or the load elements L in circuit l2! below the peak value to maintain the heater connected.

The peak value may be varied within limits by varying the adjustment of the screw 8|. By adjusting the screw downward, thereby increasing the pressure of the finger H on the switch lever 55, the peak value may be reduced, and by adjusting the screw upward, the peak value may be raised. Suitable indicia indicating the peak values that may be set may be scribed on the head 89 and read in conjunction with pin 91 as an index.

As shown in Fig. 5, the heater H is connected in the circuit on the supply side of the current limiter, and the current drawn by the heater has no effect on the current limiter. That is, the current limiter is solely responsive to current flow in the leg of the circuit in which the E-shaped thermostatic device is connected. The w switch 49 efiects solely the operation of the water heater H (secondary load element).

The central thermostatic leg 13 of the E- shaped thermostatic device does not carry current, being electrically as well as thermally insulated from the member 39 by the insulation block 45. This thermal insulation of the leg 13 from the member 39 is important because it prevents leg 73 from being heated by conduction and changing the operating characteristics. central leg 13 acts as a switch-operating arm and i made thermostatic to ailord ambient temperature compensation by reason of the fact that as member 39 moves in response to ambient temperature changes, the end of the leg 13 moves 1 in such direction as to counteract the movement of the member 39. For example, if the ambient temperature increases and member 39 moves upward in switch-opening direction, the free end of leg 13 moves upward to offset the tendency of member 39 to open the switch. The leg 13 is made thicker than the legs 35 and 31 as it bears a greater mechanical load and its length is made such as to afford the necessary deflection of its free end for ambient temperature compensation. The hinging of the leg 13 to the member 39 is an important feature as it has the advantage of eliminating the effect of any difference between the temperature-displacement characteristics of legs 35 and 31.

Cross reference is made to my copending divisional application entitled Current Limiter, Serial No. 145,227, filed February 20, 1950.

In view of the above, it will be seen that the The several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above electrical load connected across the neutral and one outer leg, another primaryv electrical load connected across the neutral and the other vouter leg, the net load on each outer leg being approximately the same, a current limiter comprising a current heated thermostatic device and a switch mechanically coupled thereto for operation upon flow of a predetermined value of current, "said thermostatic device being connected in only one of the outer legs of the wiring system. and a secondary load element connected to said one outer leg on the supply side of the thermostatic device in a line including said switch, said thermostatic device being solely responsive to current flow in one outer leg to the primary loads and said switch efieoting solely the operation of said secondary load element.

2. In a three-wire single-phase wiring system having a neutral and two outer legs, a primary electrical load connected across the neutral and one outer leg, another primary electrical load connected across the neutral and the other outer leg, the net load on each outer leg being approximately the same, and a current limiter comprising a current heated thermostatic device and a switch mechanically coupled thereto for operation upon ilow of a predetermined value of current, said thermostatic device being connected in one of the outer legs of the wiring system, and

a secondary load element connected across the two outer legs on the supply side of the thermostatic device in a line including said switch, said thermostatic device being solely responsive to current flow to the primary loads and said switch effecting solely the operation of said secondary load element.

3. In a three-wire single-phase wiring system having a neutral and two outer legs, a primary electrical load connected across the neutral and one outer leg, another primary electrical load connected across the neutral and the other outer leg, the net load on each outer leg being approximately the same, a primary load element connected across the outer legs, and a current limiter comprising a current heated thermostatic device and a switch mechanically coupled thereto for operation upon flow of a predetermined value of current, said thermostatic device being connected in only one of the outer legs of the wiring system, and a secondary load element connected across the outer legs on the supply side of the thermostatic device in a line including said switch, said thermostatic device being solely responsive to current flow in said one outer leg to the said primary loads and the primary load element and said switch effecting solely the operation of said secondary load element.

4. In a three-wire single-phase wiring system having a neutral and two outer legs, a primary electrical load connected across the neutral and one outer leg, another primary electrical load connected across the neutral and the other outer leg, the net load on each outer leg being approximately the same, a primary load element conflow:- of: a, predetermined; vazliiem. of current; said 5 thermostatic-device.beingsconneeted in one of the enters-legs of: the-wiringrisystem, andtaasecondary load element connected across" saidilegs-c on the supply side of the thermostatic device inia l'ine including sai'diswitch; said thermostatic device being: solelyxresponsive to: current :fi'ew to the said primary-loads: and the :pri-marw ieadelement and:

said switch" efi ecting -solely the opexratioit- 0f" said:

secondary load element:-

VERNON A SANDERS. 15?

REFERENGES CITED The follbwing" references areof record iii the me: of {tfiisi patent:

UNITED' STATES PATENTS- 

